After a rough summer, Hillary Clinton's advantages in experience and composure were clear when she shared a stage with her rivals for the first time, says The Post's Dana Milbank. (Tom LeGro/The Washington Post)

After Sanders and Chafee criticized her 2003 Iraq vote — reviving a rather old issue — Clinton replied: “Well, I recall very well being on a debate stage, I think, about 25 times with then-Senator Obama, debating this very issue. After the election, he asked me to become secretary of state.”

When O’Malley criticized her for being too quick to use the military, Clinton responded: “You know, I have to say, I was very pleased when Governor O’Malley endorsed me for president in 2008, and I enjoyed his strong support in that campaign.”

She parried with relative ease, refusing to allow moderator Anderson Cooper of CNN and her rivals to get under her skin. She scored points on most of the key Democratic issues — paid sick and family leave, equal pay, gun control, Planned Parenthood, executive pay — and she deflected criticism of her changing views on trade and energy, and her response to the Benghazi attack. She turned Cooper’s question about her e-mail into the highlight of the night.

While repeating that her private e-mail server was a “mistake,” she said the House committee that exposed the issue was “a partisan vehicle, as admitted by the House Republican majority leader, Mr. McCarthy, to drive down my poll numbers.” She added: “I am still standing.”

Sanders, invited to criticize Clinton, instead leaped to her defense. “I think the secretary is right, and that is that the American people are sick and tired of hearing about your damn e-mails,” he said.

Clinton dispatched Chafee as if brushing lint from her sleeve. Asked if she wanted to respond, she replied: “No.”

She was, in short, a man among boys. And that’s why the debate was so important to Clinton. She may have had a rough time as the Democrats’ presidential front-runner, but her advantages in experience and composure were clear when she shared a stage with her rivals for the first time. Vice President Biden, if he was still pondering a run while watching the debate on television, would find the rationale for his candidacy diminishing.

A month ago she was in “free fall” and “plunging” in the polls, giving those who watched her campaign collapse in 2008 a sense of déjà vu. Sanders was closing in, the draft-Biden movement was in full force, and Republicans were giddy with anticipation of her upcoming grilling by the House Benghazi committee.

But a mass shooting in Oregon put the gun-friendly Sanders on the defensive. The Obama administration’s completion of a Pacific trade deal, deeply unpopular on the left, puts Biden on the wrong side of the Democratic electorate on an issue that should be prominent in the headlines over the coming months. And the House Benghazi panel has been discredited by Majority Leader Kevin McCarthy’s incautious admission that the committee was created to damage Clinton politically. Now polls show Clinton recovering and expanding her lead — and if the Tuesday debate is any indication, this will likely continue.

Sanders, her nearest rival in the polls, gesticulated wildly through the night and shouted in his Brooklyn accent about the wrongs of millionayuhs and billionayuhs.

Cooper captured the problem with the Sanders candidacy when he said: “The Republican attack ad against you in a general election — it writes itself. You supported the Sandinistas in Nicaragua. You honeymooned in the Soviet Union. And just this weekend, you said you’re not a capitalist.”

Sanders did not help himself by talking about the economic example of Denmark and proclaiming that he’s “going to win because we’re going to explain what Democratic socialism is.”

Replied Clinton: “We are not Denmark. . . . We are the United States of America. And it’s our job to rein in the excesses of capitalism so that it doesn’t run amok and doesn’t cause the kind of inequities we’re seeing in our economic system. But we would be making a grave mistake to turn our backs on what built the greatest middle class in the history of the world.”

He defended socialism; she defended the middle class. Sanders, and the other men on the stage, didn’t look presidential; she did.